The present invention relates to an internal combustion engine (hereinafter, referred to simply as an engine) having an evaporated fuel purge system. This evaporated fuel purge system is adapted to allow, fuel vapor produced in a fuel tank to be directly sucked into an intake pipe of the engine in order to dispose of the fuel vapor.
A conventional example of a control method for purging evaporated fuel in a fuel tank or the like is disclosed in, for example, Japanese Patent Unexamined Publication No. 57-52663. Most of conventional evaporated fuel disposal systems, including the system disclosed in the above publication, are provided with charcoal canisters and are adapted to cause fuel vapor produced in fuel tanks to be once adsorbed by active carbon within the charcoal canisters. The fuel vapor thus adsorbed is discharged from the charcoal canisters and sucked into combustion chambers of engines at the time when the fuel vapor will not exert bad influence on the operation of the engines even if the fuel vapor is additionally mixed with intake air, for instance, at the time when the engines are driven under high load. In other words, in the engines with the conventional systems of this kind, the charcoal canisters are used for storage of the evaporated fuel even during the engines are running.
In the conventional system, as described above, the evaporated fuel is once stored in the charcoal canister even when the engine runs, and only when the engine comes into an operating state which is suitable for purging the evaporated fuel, a valve provided on a purge pipe is opened for allowing the fuel vapor to be sucked from the charcoal canister into combustion chambers of the engine. Thus, the charcoal canister is required to have a sufficiently large adsorption capacity, and it is generally difficult to form the canister into a compact size. Also, deterioration in adsorbing ability of the active carbon is a matter to be considered because the canister has to continuously adsorb the fuel vapor. Further, in the case where an amount of production of the evaporated fuel exceeds the adsorption capacity of the canister, there is a possibility that the fuel vapor will be directly discharged to the atmosphere.